Altering method of circuit pattern of printed-circuit board, cutting method of circuit pattern of printed-circuit board and printed-circuit board having altered circuit pattern

ABSTRACT

A method for altering a circuit pattern of a printed-circuit board includes the steps of removing a portion of the printed-circuit board so that the circuit pattern inside the printed-circuit board is exposed, and connecting an exposed portion of the circuit pattern to another portion of the printed-circuit board by a conductive body so that a circuit path is formed between the exposed portion of the circuit pattern and the other portion of the printed-circuit board.

This is a Division of application Ser. No. 08/711,656 filed Sep. 9, 1996now U.S. Pat. No. 6,415,504. The disclosure of the prior application(s)is hereby incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention generally relates to methods for altering andcutting circuit patterns of a printed-circuit board and aprinted-circuit board, and more particularly to an altering method foraltering a circuit pattern on an inner layer of a multi-layerprinted-circuit board (an organic printed-circuit board, such as aglass-epoxy board and a polyimide board, and an inorganicprinted-circuit board, such as a ceramic board), a cutting method forcutting a circuit pattern of a printed-circuit board, applicable to thealtering method, and a printed-circuit board having an altered circuitpattern.

(2) Description of the Related Art

Conventionally, in a printed-circuit board in which a circuit patterncorresponding to electronic circuits for electronic equipment is formed,spare circuit lines, spare connecting pads, spare via-holes used toelectrically connecting circuit patterns on stacked layers and the likeare often additionally formed for alteration of the circuit patternbased on design changes of the electronic circuits. When the designchanges of the electronic circuits have been made, a new circuit patterncan be formed using the spare circuit lines, the spare connecting padsand the spare via-holes. In addition, the circuit pattern correspondingto the original electronic circuits is cut so as to be altered into acircuit pattern corresponding to the design changed electronic circuits.

Due to the use of such printed-circuit boards, even if the designchanges of the electronic circuits are made, it is not necessary to makea new printed-circuit board corresponding to the design changedelectronic circuits. Thus, the printed-circuit board having the circuitpattern corresponding to the design changed circuits can be rapidlyprepared.

On the other hand, in recent years, printed-circuit boards have beenminiaturized by increasing the density of the circuit pattern. Thus,since forming of the spare circuit lines, the spare connecting pads andthe spare via-holes prevents the density of the circuit pattern frombeing increased, there is a tendency to abandon formation of these spareelements.

However, in a case where a printed-circuit board from which the spareelements, such as the spare circuit lines, the spare connecting pads andthe spare via-holes are omitted is used, it is difficult to alter acircuit pattern on an inner layer of the printed-circuit board when thedesign changes of the electronic circuits have been made.

In addition, in a case where the circuit pattern on the inner layer ofthe printed-circuit board is altered, the circuit pattern is generallycut. In this case, the circuit pattern on the inner layer of theprinted-circuit board has to be accurately cut with consideration to aposition of an adjacent circuit pattern. In particular, in a case wherethe circuit is cut, in a non-contacting manner, using a high energybeam, such as an electron beam or a laser beam, metal powder generatedby the abrasion of material of the circuit pattern causes insulationdefects. The insulation defects must be prevented.

SUMMARY OF THE INVENTION

Accordingly, a general object of the present invention is to providemethods for altering and cutting a circuit pattern of a printed-circuitboard and a printed-circuit board having an altered circuit pattern, inwhich the disadvantages of the aforementioned prior art are eliminated.

A first specific object of the present invention is to provide analtering method which can easily alter a circuit pattern on an innerlayer of a printed-circuit board.

The above objects of the present invention are achieved by a method foraltering a circuit pattern of a printed-circuit board, comprising thesteps of: (a) removing a portion of the printed-circuit board so thatthe circuit pattern inside the printed-circuit board is exposed; and (b)connecting an exposed portion of the circuit pattern obtained in step(a) to another portion of the printed-circuit board by a conductive bodyso that a circuit path is formed between the exposed portion of thecircuit pattern and the another portion of the printed-circuit board.

According to the altering method of the present invention, a new circuitpath which connects the circuit pattern to another portion of theprinted-circuit board can be formed without spare circuit lines, sparelands and the like.

A second specific object of the present invention is to provide acutting method by which a circuit pattern can be accurately cut inconsideration of a position of another circuit pattern.

The above object of the present invention is achieved by the followingmethods:

A method for cutting a circuit pattern located under a sheet-shapedcircuit pattern inside a printed-circuit board comprising the steps of(a) forming a first cutting hole which passes through the sheet-shapedcircuit pattern, the first cutting hole having a first aperture area,and (b) forming a second cutting hole which expands from a bottomsurface of the first cutting hole and passes through the circuit patternso that the circuit pattern is cut, the second cutting hole having asecond aperture area narrower than the first aperture area;

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the steps of (a) removing a portion with a predetermineddepth of the printed-circuit board, and (b) expanding the portion whichis removed in a direction parallel to the surface of the printed-circuitboard, so that the circuit pattern is cut while the portion which isremoved is being expanded;

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the steps of (a) adjusting a mask of a beam so that aprojection area of the beam projected onto a surface of theprinted-circuit board has a predetermined length in a direction parallelto a width direction of the circuit pattern, and (b) projecting the beamonto the printed-circuit board so that a hole is formed in theprinted-circuit board, whereby the circuit pattern is cut by the beam;

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the steps of (a) adjusting a mask of a beam having apredetermined energy so that a projection area of the beam is formed ona surface of the printed-circuit board, the projection area beingdecided based on a narrowing ratio of the beam and a working area of thebeam projected onto a surface of the circuit pattern to be cut, thenarrowing ratio of the beam being a degree of narrowing of an area, tobe worked by the beam having the predetermined energy, in materials onand over a surface of the circuit pattern, and (b) projecting the beamin which the mask thereof is adjusted on the printed circuit board sothat a hole is formed in the printed-circuit board, whereby the circuitpattern is cut by the beam;

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the steps of (a) removing a portion of the printed-circuitboard by projection of a beam focused on a focal point, and (b) movingthe focal point on which the beam is focused with moving of a workingarea of the beam inside the printed-circuit board caused by removal ofthe portion of the printed-circuit board, whereby the circuit pattern iscut by the beam;

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the steps of (a) projecting a beam in which a mask thereof isadjusted so that a first projection area of the beam corresponds to anarea covering the circuit pattern, a first portion at a first side ofthe circuit pattern and a second portion at a second side of the circuitpattern, a hole being formed by the beam until a predetermined depth isobtained, (b) projecting the beam in which the mask thereof is adjustedso that a second projection area of the beam corresponds to an areacovering the circuit pattern and the first portion, and (c) projectingthe beam in which the mask thereof is adjusted so that a thirdprojection area of the beam corresponds to an area covering the circuitpattern and the second portion, wherein after the step (a) is completed,the step (b) and the step (c) are alternately repeated at predeterminedintervals until the circuit pattern is cut by the beam; and

A method for cutting a circuit pattern inside a printed-circuit boardcomprising the step of projecting a beam on the printed-circuit boardwhile a mask thereof is being adjusted so that a projection area of thebeam is narrowed, a hole being formed in the printed-circuit board byprojection of the beam, so that the circuit pattern is cut by the beam.

According to the cutting method of the present invention, the circuitpattern can be accurately cut while taking into consideration of aposition of another circuit pattern such as the sheet-haped circuitpattern.

A third specific object of the present invention is to provide aprinted-circuit board having an altered circuit pattern.

The above object of the present invention is achieved by aprinted-circuit board comprising: a circuit device mounted on theprinted circuit board; and a conductive body which is in a groove formedin the printed-circuit board so as to pass under the circuit device, thegroove corresponding to a circuit path.

According to the printed-circuit board of the present invention, theprinted-circuit board in which a circuit pattern has been altered can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beapparent from the following description when read in conjunction withthe accompanying drawings, in which:

FIGS. 1A, 1B, 1C and 1D are diagrams illustrating a process for alteringa circuit pattern of a printed-circuit board according to an embodimentof the present invention;

FIG. 2 is a diagram illustrating an example of a worked hole or openingformed on the printed-circuit board to alter the circuit pattern on aninner layer;

FIG. 3 is a diagram illustrating another example of the worked hole oropening;

FIGS. 4A, 4B and 4C are diagrams illustrating a process for connecting awire to the exposed circuit pattern;

FIGS. 5A, 5B and 5C are diagrams illustrating another process forconnecting a wire to the exposed circuit pattern;

FIGS. 6A and 6B are diagrams illustrating an example of a position atwhich the circuit pattern is exposed;

FIGS. 7A and 7B are diagrams illustrating another example of a positionat which the circuit pattern is exposed;

FIG. 8 is a diagram illustrating a position at which the circuit patternunder a sheet-shaped circuit pattern in the printed-circuit board isexposed;

FIGS. 9A and 9B are diagrams illustrating a process for forming the holethrough which the circuit pattern is exposed at the position shown inFIG. 8;

FIGS. 10A, 10B and 10C are diagrams illustrating a process forconnecting a wire to the circuit pattern exposed through the hole asshown in FIGS. 8, 9A and 9B;

FIG. 11 is a diagram illustrating a position at which the circuitpattern located under a sheet-shaped circuit pattern in theprinted-circuit board is exposed;

FIGS. 12A, 12B and 12C are diagrams illustrating a process for forming ahole through which the circuit pattern is exposed at the position shownin FIG. 11;

FIGS. 13A, 13B and 13C are diagrams illustrating a process for cuttingthe circuit pattern located under a sheet-shaped circuit pattern in theprinted-circuit board;

FIG. 14 is a diagram illustrating examples of holes mechanically formedto cut the circuit pattern inside the printed-circuit board;

FIG. 15 is a diagram illustrating holes improved in comparison with theholes shown in FIG. 14;

FIG. 16 is a diagram illustrating examples of holes formed using a highenergy beam to cut the circuit pattern inside the printed-circuit board;

FIG. 17 is a diagram illustrating holes improved in comparison with theholes shown in FIG. 16;

FIG. 18 is a diagram illustrating holes having widths which areacceptable to cut the circuit pattern inside the printed-circuit board(1st);

FIG. 19 is a diagram illustrating holes having widths which areacceptable to cut the circuit pattern inside the printed-circuit board(2nd);

FIG. 20 is a cross sectional view illustrating a structure of a holeformed to cut the circuit pattern inside the printed-circuit board;

FIG. 21 is a cross sectional view illustrating a hole formed using abeam and a focus point of the beam;

FIG. 22 is a cross sectional view illustrating a hole formed using abeam in which a focus point is adjusted;

FIGS. 23A and 23B are diagrams illustrating an example of a mask for abeam used to cut the circuit pattern inside the printed-circuit board;

FIGS. 24 and 24B are diagrams illustrating a procedure for adjusting amask for a beam used to cut the circuit pattern inside theprinted-circuit board;

FIG. 25 is a cross sectional view illustrating the circuit pattern cutby the beam for which the mask is adjusted as shown in FIG. 24 (1st);

FIG. 26 is a cross sectional view illustrating the circuit pattern cutby the beam for which the mask is adjusted as shown in FIG. 24 (2nd);

FIGS. 27A and 27B are diagrams illustrating another example of a maskingadjustment for the beam used to cut the circuit pattern inside theprinted-circuit board and a cross sectional structure of a hole formedof the beam;

FIGS. 28A and 28B are diagrams illustrating a mask for a beam used toremove metal powder from the hole formed to cut the circuit pattern asshown in FIGS. 27A and 27B and a cross sectional structure of the holefrom which the metal powder is removed;

FIGS. 29A and 29B are diagrams illustrating another example of a maskingadjustment for the beam used to cut the circuit pattern inside theprinted-circuit board and a cross sectional structure of a hole formedof the beam;

FIGS. 30A and 30B are diagrams illustrating a mask for a beam used toremove metal powder from the hole formed to cut the circuit pattern asshown in FIGS. 29A and 29B and a cross sectional structure of the holefrom which the metal powder is removed;

FIG. 31 is a diagram illustrating a structure by which a circuit wirepasses under circuit elements mounted on the printed-circuit board;

FIG. 32 is a plan view illustrating a groove in which a circuit wireconnecting circuit patterns exposed from the printed-circuit board isplaced;

FIG. 33 is a plan view illustrating a groove which is filled withconductive material connecting circuit patterns exposed from theprinted-circuit board;

FIGS. 34A and 34B are diagrams illustrating a method for fixing the wirein the groove shown in FIG. 32 (1st); and

FIGS. 35A and 35B are diagrams illustrating a method for fixing the wirein the groove shown in FIG. 32 (2nd).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of an embodiment of the present invention.

A printed-circuit board which should be altered is formed as shown inFIG. 1A. Referring to FIG. 1A, a first circuit pattern 101 which isline-shaped and a second circuit pattern 102 which is sheet-shaped areformed inside a printed-circuit board 100 (made of, for example,glass-epoxy resin). The second circuit pattern 102 is located under thefirst circuit pattern 101. The first circuit pattern 101 is used fortransmission of signals, and the second circuit pattern 102 is used fora power line or a ground line. Lands 104 and 125 are formed on aninsulating body 103 (e.g., insulating material or resist) covering thefirst circuit pattern 101. Via-holes 104 and 124 respectively extendingfrom the lands 105 and 125 to the first circuit pattern 101 are formedin the printed-circuit board 100. The via-holes 104 and 124 arerespectively filled with pins 12 and 22 of electronic components 11 and21 (e.g., LSI devices). The pins 12 and 22 electrically contact thefirst circuit pattern 101, and are fixed onto the printed-circuit board100 by solder lumps 106 and 126 on the lands 105 and 125.

The first circuit pattern 101 located over the second circuit pattern102 inside the printed-circuit board 100 as described above is alteredin accordance with a procedure as shown in FIGS. 1B, 1C and 1D.

First, as shown in FIG. 1B, holes 107 and 127 are respectively formed atpositions adjacent to the lands 105 and 125 so as to pass through thefirst circuit pattern 101. As a result, the first circuit pattern 101 iscut, so that the electrical connection between the pins 12 and 22 of theelectronic components 11 and 21 through the first circuit pattern 101 iscut off. The first circuit pattern 101 may be mechanically cut using adrill, and may be cut, in a non-contacting manner, using a high energybeam such as a laser beam or an electron beam. The detailed descriptionof cutting of the circuit pattern will be given later.

After the first circuit pattern 101 is cut as described above, theinsulating body 103 is partially removed so that pattern exposure holes108 and 128 are formed. Parts of the first circuit pattern 101 whichelectrically contact the pins 12 and 22 of the electronic components 11and 22 are partially exposed through the pattern exposure holes 108 and128. The pattern exposure holes 108 and 128 may be mechanically formedusing an end mill and may be formed, in a non-contacting manner, byusing a high energy beam such as a laser beam or an electron beam. Thedepth of each of the pattern exposure holes 108 and 128 can be knownfrom design data of the printed-circuit board 100. The depth of a cut bya mechanical cutting tool such as the end mill is controlled inaccordance with the design depth. The power of the laser beam which ispulsed and the number of projections of the laser beam are controlled sothat the holes having the above depth are formed.

For example, the laser beam emitted by an excimer laser unit is maskedso that the laser spot is squarely shaped. The laser beam is thenprojected onto the insulating body 103 of the printed-circuit board 100,so that the insulating body 103 is removed in square as shown in FIG. 2.That is, a square-shaped pattern exposure hole 108 through which thefirst circuit pattern 101 is exposed is formed. The mask of the laserbeam is adjusted so that the width of the square-shaped pattern exposurehole 108 is slightly greater than the width of the first circuit pattern101.

As shown in FIG. 3, a wire connecting pad 101 a may be formed on a partof the first circuit pattern 101, near the via-hole 104, covered withthe resist layer (the insulating body 103). In this case, the resistlayer is removed in a square by the laser beam from the excimer laserunit. As a result, the wire connecting pad 101 a is exposed through thesquare-shaped pattern exposure hole 108. The mask of the laser beam isadjusted so that the spot area of the laser beam is slightly greaterthan the area of the wire connecting pad 101 a.

After the parts of the first circuit pattern 101 connected with the pins12 and 22 of the electronic components 11 and 21 are partially exposedas described above, electric connection bodies 109 and 129 arerespectively formed on the exposed parts of the firs circuit pattern 101(the pattern exposure holes 108 and 128). The electric connection bodies109 and 129 are then connected to each other by a wire 30. As a result,the pins 12 and 22 of the electronic components 11 and 21 areelectrically connected to each other via the wire 30. That is, the firstcircuit pattern 101 is altered so that the pins 12 and 22 of theelectronic components 11 and 21 are disconnected from other electroniccomponents connected to the first circuit pattern 101 and are directlyconnected to each other.

Each of the electric connection bodies 109 and 129 is formed in thepattern exposure hole through which the first circuit pattern 101 isexposed, as shown in FIGS. 4A, 4B and 4C. FIGS. 4A, 4B and 4C show acase where the electric connection body is formed in the patternexposure hole 108. The electric connection body is also formed in thepattern exposure hole 128 in the same manner as in this case.

The pattern exposure hole 108 though which the first circuit pattern 101is exposed is filled with soldering paste 300 (a conductive connectingbody) (see FIGS. 4A and 4B). A core 32 projecting from a cover 31 of thewire 30 is then inserted into the soldering paste 300 (see FIG. 4B). Inthis state, the soldering paste 300 is melted by hot-air heat, CO₂ laserbeam or the like. After this, the soldering paste 300 which has beenmelted is hardened (see FIG. 4C). As a result, the electric connectionbody 109 having a structure in which the core 32 of the wire 30 iselectrically connected to the first circuit pattern 101 by the solder300 is formed in the pattern exposure hole 108.

Solder wire, solder ribbon, solder plate and solder ball may be used inplace of the soldering paste 300. Further, conductive adhesive may beused as the conductive connecting body in place of the solder.

The electric connection body may be formed in accordance with aprocedure shown in FIGS. 5A, 5B and 5C.

In this case, a solder lump 300 is attached to the core 32 projectingfrom the cover 31 of the wire 30 in accordance with a method of thescreen deposition. The solder lump 300 has a volume which can be placedin the pattern exposure hole 108 and is enough to form a pertinentelectric connection body. The tip end of the wire 30 to which the solderlump 300 is attached is inserted into the pattern exposure hole 108through which the first circuit pattern 101 is exposed (see FIGS. 5A and5B). In this state, the solder lump 300 is heated so as to be melted inthe pattern exposure hole 108 (see FIG. 5C). The solder which has beenmelted is hardened, so that the electric connection body is formed inthe pattern exposure hole 108.

As has been described above, a circuit pattern is partially exposed toalter the circuit pattern of the multi-layer printed-circuit board(forming of the pattern exposure holes 108 and 128). In this case, caremust be taken that other circuit patterns located near the circuitpattern to be altered are not damaged. FIG. 6A shows a portion near aposition at which the pattern exposure hole is formed. FIG. 6B is across sectional view taken along line A—A shown in FIG. 6A. In a caseshown in FIGS. 6A and 6B, other circuit patterns 111 and 112 are locatedover the circuit pattern 101 which is to be exposed. If a patternexposure hole H is formed at a position near a pin of an electroniccomponent inserted into the via-hole 104, the pattern exposure hole Hinterferes with the circuit pattern 111. Thus, the pattern exposure holeH can not be formed at the position. In this case, it is decided, basedon the design data of the printed-circuit board 100, that a patternexposure hole 108 a is formed at a position in an area between the othercircuit patterns 111 and 112.

When design changes regarding the power line or the ground line aremade, the sheet-shaped circuit pattern 102 used for the power line orthe ground line is altered. In this case, the sheet-shaped circuitpattern (the second circuit pattern) 102 is partially exposed and anexposed part of the sheet-shaped circuit pattern 102 is connected to adesired portion by a wire in the same manner as in the case of the firstcircuit pattern 101.

Since the sheet-shaped circuit pattern 102 has a relatively wide area, aposition at which the pattern exposure hole should be formed can beroughly decided in comparison with the case of the line-shaped circuitpattern (the first circuit pattern) 101. However, in a case where thesheet-shaped circuit pattern 102 is located in a deep layer, line-shapedcircuit patterns may be complicatedly located over the sheet-shapedcircuit pattern 102. Thus, care must be taken that circuit patternslocated over the sheet-shaped circuit pattern are not damaged.

FIG. 7A shows a portion near a position at which the pattern exposurehole for the sheet-shaped circuit pattern 102 is formed. FIG. 7B is across sectional view taken along line A—A shown in FIG. 7A. If a patternexposure hole H is formed at a position near a pin of an electroniccomponent inserted into the via-hole 104, the pattern exposure hole Hinterferes with the circuit pattern 101 and 111 located over thesheet-shaped circuit pattern 102. Thus, the pattern exposure hole H cannot be formed at the position. In this case, it is decided, based on thedesign data of the printed-circuit board 100, that a pattern exposurehole 108 a is formed at a position in an area surrounded by circuitpatterns 111, 112, 101 and 101′.

For example, a circuit pattern located under the sheet-shaped circuitpattern 102 is partially exposed, an exposed part of the circuit patternis connected to another portion by the wire. In this case, the patternexposure hole for the circuit pattern passes through the sheet-shapedcircuit pattern 102 and reaches the circuit pattern. The patternexposure hole may be formed by the laser beam from the excimer laserunit. When the laser beam passes through (partially removes) thesheet-shaped circuit pattern 102, metal powder caused by the abrasion ofmaterial (copper) of the sheet-shaped circuit pattern 102 is adhered toan inner wall of the pattern exposure hole. Thus, if the patternexposure hole is formed so as to reach the circuit pattern to be exposedstraight out, the sheet-shaped circuit pattern 102 and the circuitpattern which is located under the sheet-shaped circuit pattern 102 andis to be exposed may be short-circuited by the metal powder (insulationdefects).

To prevent the short circuit between the sheet-shaped circuit pattern 12and the circuit pattern to be exposed, it is preferable that the patternexposure hole for the circuit pattern located under the sheet-shapedcircuit pattern is formed in accordance with a procedure as shown inFIGS. 8, 9A and 9B. FIG. 8 is a plan view showing a portion in which thepattern exposure hole should be formed. FIGS. 9A and 9B are crosssectional views taken along line A—A shown in FIG. 8.

A position on a plane at which the pattern exposure hole 108 for acircuit pattern 114, located under the sheet-shaped circuit pattern 102,is decided as shown in FIG. 8, based on the design data of theprinted-circuit board 100. That is, the position of the pattern exposurehole 108 on the plane is decided so that the pattern exposure hole 108does not interfere with all the circuit patterns 111, 112, 101 and 101′located over the sheet-shaped circuit pattern 102.

The laser beam from the excimer laser unit is masked so as to have asquare-shaped beam spot. The pulsed laser beam is projected at theposition, decided as described above, on the surface of the insulatingbody 103 of the printed-circuit board 100. The mask of the laser beam isadjusted so that the laser beam spot formed on the surface of theinsulating body 103 has a first area. The insulating body 103 is removedby the pulsed laser beam projected from the excimer laser unit onto theinsulating body 103. As a result, as shown in FIG. 9A, a first hole108(1) having a square-shaped cross section is formed. That is, thelaser beam passes through the sheet-shaped circuit pattern 102, and thefirst hole 108(1) having a predetermined depth D1 is formed. Theintensity of the laser beam and the number of times which the laser beamis projected (the number of pulses) are decided, based on the materialof the insulating body 103 and the sheet-shaped circuit pattern 102, sothat the depth D1 of the first hole 108(1) is slightly greater than thelength between the surface of the insulating body 103 and thesheet-shaped circuit pattern 102.

Next, the mask of the laser beam is adjusted so that the area of thelaser beam spot is changed from the first area to a second area which isnarrower than the first area. In this state, the pulsed laser beam isfurther projected onto a bottom surface of the first hole 108(1). As aresult, as shown in FIG. 9B, a second hole 108(2) expanding from thebottom surface of the first hole 108(1) to the circuit pattern 114 isformed. The depth D2 of the second hole 108(2) corresponds to thedifference between the length from the surface of the insulating body103 to the circuit pattern 114 and the depth D1 of first hole 108(1).Thus, the intensity of the laser beam and the number of times which thelaser beam is projected (the number of pulses) decide the depth of thesecond hole 108(2) is equal to D2 corresponding to the above difference.

The aperture area of the second hole 108(2) (corresponding to the secondarea of the laser beam spot) is decided, as shown in FIG. 8, so as tohave enough area to form the electric connection body on the exposedportion of the circuit pattern 114. The aperture area of the first hole108(1) (corresponding to the first area of the laser beam spot) isdecided so as to be slightly greater than the second area. Thus, thepattern exposure hole 108 through which the circuit pattern 114 locatedunder the sheet-shaped circuit pattern 102 is exposed has a structure inwhich there is a step in a boundary between the first hole 108(1) andthe second hole 108(2).

In the case where the pattern exposure hole 108 (the first and secondholes 108(1) and 108(2) is formed by switching the laser beam spot areain two steps, the metal powder of the sheet-shaped circuit pattern 102may be adhered to the wall of the first hole 108(1). However, sinceafter the first hole 108(1) passes through the sheet-shaped circuitpattern 102, the second hole 108(2) is formed, the metal powder is notadhered to the wall of the second hole 108(2). Thus, the insulationdefects between the circuit pattern 114 and the sheet-shaped circuitpattern 102 located above the circuit pattern 114 can be prevented.

After the pattern exposure hole 108 through which the circuit pattern114 located under the sheet-shaped circuit pattern 102 is exposed isformed as described above, the electric connection body is formed on theexposed potion of the circuit pattern 114 in accordance with a procedureas shown in FIGS. 10A, 10B and 10C. The electric connection body isfixed with a tip end of a wire used to electrically connect to anotherportion.

The core 32 projecting from the cover 31 of the wire 30 is plated withsolder so that a solder plating layer 301 covers the core 32 of the wire30. The core 32 projecting from the cover 31 is bent at 90°. In thisstate, the core 32 of the wire 30 is inserted into the pattern exposurehole 108 formed as described above (see FIGS. 10A and 10B). The core 32which is bent at 90° and plated with solder is pressed against thecircuit pattern 114 by the reflow-chip 400. In this state, the core 32is heated by hot-air (see FIG. 10C). The solder plating layer 301covering the core 32 is thus melted. After the hot-air supplied to thecore 32 is stopped, the solder which has been melted is hardened. As aresult, the core 32 is electrically connected to the circuit pattern 114by the solder 301. The wire 30 connected to the circuit pattern 114 isdrawn out of the pattern exposure hole 108, and another end of the wire30 is connected to a predetermined portion of the printed-circuit board100.

In the above case, the second hole 108(2) has to have enough aperturearea to insert the core 32 which is bent into the second hole 108(2).The depth D2 of the second hole 108(2) is decided so that the core 32projecting from the cover 31 of the wire 30 is not in contact with thesheet-shaped circuit pattern 102.

To positively prevent the metal powder generated when the sheet-shapedcircuit pattern 102 is partially removed by the laser beam from causingthe insulation defects between the sheet-shaped circuit pattern 102 andthe circuit pattern 114, the pattern exposure hole 108 may be formed inaccordance with a procedure as shown in FIGS. 11, 12A, 12B and 12C. FIG.11 is a plan view showing a portion near a position at which the patternexposure hole is formed. FIGS. 12A, 12B and 12C are cross sectionalviews taken along line A—A shown in FIG. 11.

A position on a plane at which the pattern exposure hole should beformed is decided so that the pattern exposure hole does not interferewith all circuit patterns located over the sheet-shaped circuit pattern102 (see FIG. 11), in the same manner as in the case shown in FIG. 8.The pulsed laser beam from the excimer laser unit is masked so as tohave the square-shaped spot of the first area. The pulsed laser isprojected at the position, decided as described above, on the insulatingbody 103, so that the first hole 108(1) is formed (see FIG. 12A), in thesame manner as in the case shown in FIG. 9A. The first hole 108(1)passes through the sheet-shaped circuit pattern 102.

After this, as shown in FIG. 12B, the first hole 108(1) formed asdescribed above is filled with insulating resin 150. The mask of thelaser beam from the excimer laser unit is adjusted so that the laserbeam spot is changed from the first area to the second area which isnarrower than the first area. In this state, the pulsed laser beam isprojected on to the insulating resin 150. A portion of the insulatingresin 150 corresponding to the laser beam spot having the second area isremoved by the laser beam. As a result, a hole is formed concentric withthe first hole 108(1). After the laser beam passes through theinsulating resin 150, the projection of the laser beam is continued. Asecond hole 108(2) having an aperture of the second area is formed fromthe bottom surface of the insulating resin 150 to the circuit pattern114 (see FIG. 12C).

As the result of the above process, the first hole 108(1) in which theinner surface is coated with the insulating resin 150 and the secondhole 108(2) in which the inner surface is not coated with the insulatingresin form the pattern exposure hole 108.

According to the above manner in which the pattern exposure hole 108 forthe circuit pattern 114 located under the sheet-shaped circuit pattern102 is formed, even if metal powder is generated while the first hole108(1) is being formed, the cutting surface of the sheet-shaped circuitpattern 102 and the generated metal powder are covered with theinsulating resin 150. Thus, even if the hole is formed from theinsulating resin 150 to the surface of the circuit pattern 114 to beexposed, the electrical insulation between the circuit pattern 114 andthe sheet-circuit pattern 102 is reliably maintained.

Further, in a case where the circuit pattern 114 located under thesheet-shaped circuit pattern 102 is cut, it is preferable that thecircuit pattern 114 is cut by forming a stepped hole in the same manneras in the case shown in FIGS. 9A and 9B.

As shown in FIGS. 13A, 13B and 13C, the pulsed laser beam, having asquare-shaped beam spot, from the excimer laser unit is projected ontothe surface of the insulating body 103 covering the sheet-shaped circuitpattern 102. First, the mask of the laser beam is adjusted so that thesquare-shaped beam spot has a first area. A first hole 107(1) whichpasses through the sheet-shaped circuit pattern 102 is formed (see FIGS.13A and 13B). After this, the mask of the laser beam is adjusted so thatthe square-shaped beam spot has a second area less than the first area.In this state, the pulsed laser beam is further projected onto theinsulating body 103. As a result, a second hole which cuts the circuitpattern 114 is formed (see FIG. 13C).

As has been described above, a cutting hole for cutting the circuitpattern 114 located under the sheet-shaped circuit pattern 102 is formedof the first hole 107(1) which passes through the sheet-shaped circuitpattern 102 and the second hole 107(2) having an aperture area less thanthat of the first hole 107(1). As a result, the insulation defectsbetween the sheet-shaped circuit pattern 102 and the circuit pattern 114which is cut can be prevented.

In a case where a circuit pattern of the printed-circuit board isaltered, the circuit pattern is generally cut. The circuit pattern(formed on or inside the printed-circuit board) is cut by using amechanical tool (e.g. a drill) or by using a high energy beam such asthe laser beam or the electron beam in the non-contact manner. Adetailed description will now be given of high-quality methods forcutting the circuit pattern of the printed-circuit board.

As shown in FIG. 14, in a case where a circuit pattern 117 betweencircuit patterns 115 and 116 is mechanically cut by using a tool such asa drill, it is ideal that the center of a cutting hole 131 a formed bythe tool is positioned on the center line of the circuit pattern 117. Inthis ideal case, a gap between cut ends of the circuit pattern 117 has auniform value of W1. However, when the center of a cutting hole 131 bformed by the tool is shifted by δ from the center line of the circuitpattern 117, the gap between the cut ends of the circuit pattern 117 isnon-uniform as shown in FIG. 14. For example, at a side of the circuitpattern 117, the gap has a value of W21, and at an opposite side of thecircuit pattern 117, the gap has a value of W22 greater than W21. If thecenter of the cutting hole 131 b is shifted too much from the centerline of the circuit pattern 117 a side of the circuit pattern 117 maynot be completely cut.

Thus, to cut the circuit pattern 117 so that the gap between the cutends of the circuit pattern 117 is uniform even if the center of acutting hole is slightly shifted from the center line of the circuitpattern 117, the cutting hole in which a cross section is worked into anextended-circular shape is formed as shown in FIG. 15. In this case,data regarding positions, widths, inclinations and the like of thecircuit pattern to be cut are extracted from design data of theprinted-circuit board, image recognition results, results of directobservation or the like. An insert start position, an insertion depth, amoving direction and a moving distance of the tool such as the drill arethen decided based on the above extracted data. After this, drillingwork starts at the insert start position. After the tool reaches thedecided insertion depth, the tool is moved in the decided movingdirection by the decided moving distance. The printed-circuit board maybe moved, instead of the tool, in a direction opposite to the decidedmoving direction. As a result, the cutting hole 132 a has a crosssection which is an extended-circular shape as shown in FIG. 15. Thecircuit pattern 117 is cut by the cutting hole 132 a.

The moving direction is set, for example, so as to be parallel to thewidth direction of the circuit pattern 117 to be cut. In this case, evenif the center of the cutting hole 132 a is slightly shifted (by δ) fromthe center line of the circuit pattern 117, the gap between the ends ofthe cut circuit pattern 117 is uniform (W1=W2).

The moving direction may not be parallel to the width direction of thecircuit pattern 117. The moving direction is decided so that the circuitpattern is completely cut by the tool moved by the decided distance. Inaddition, the moving distance is not less than the width W1 of thecircuit pattern 117 to be cut as shown in FIG. 18. The moving distanceis decided so that other circuit patterns located in the same layer asthe circuit pattern 117 and located over the circuit pattern 117 are notbroken by the cutting hole. That is, the moving distance is decided sothat the length L2 of the aperture of the cutting hole 132 (132′) isless than the distance W2 between the circuit patterns 115 and 116between which the circuit pattern 117 to be cut is positioned, as shownin FIG. 18.

As shown in FIG. 16, in a case where a bent circuit pattern 120 putbetween bent circuit patterns 119 and 118 is cut using a laser beam inthe non-contact manner, it is ideal that the center of the square-shapedbeam spot 133 a of the laser beam is positioned on the center line ofthe circuit pattern 120. In this ideal case, the gap between cut ends ofthe circuit pattern 120 is uniform (W1) at both sides of the circuitpattern 120. However, if the square-shaped beam spot 133 b of the laserbeam is shifted by δ from the center line of the circuit pattern 120,the gap (W21) of the cut ends of the circuit pattern 120 in a sidediffers from the gap (W22) of the cut ends of the circuit pattern 120 inan opposite side (W12=W22). That is, the gap between the ends of thecircuit pattern 120 is non-uniform at both sides of the circuit pattern120. If the center of the square-shaped beam spot of the laser beam isshifted too much from the center line of the circuit pattern 120, a sideof the circuit pattern 120 may not be completely cut.

Thus, to cut the circuit pattern 120 in a state where the gap betweenthe cut ends of the circuit pattern 120 is uniform even if the beam spotof the laser beam is slightly shifted from an ideal position, the laserbeam is projected onto the circuit pattern 120 as shown in FIG. 17.Referring to FIG. 17, the angle of the mask of the laser beam isadjusted so that a projection area of the laser beam on the circuitpattern 120 is not changed even if the square-shaped beam spot of thelaser beam is slightly shifted in a predetermined direction. In anexample, data regarding the width, the inclination and the like of thecircuit pattern 120 to be cut are extracted from the design data of theprinted-circuit board, image recognition results, results of directobservation or the like. The size and the angle of the mask of the laserbeam is adjusted so that the length of the beam spot in a directionparallel to the width direction of the circuit pattern 120 is uniform.In a case shown in FIG. 17, the angle of the mask is adjusted so thattwo sides of the square-shaped beam spot are parallel to the sides ofthe circuit pattern 120 to be cut and two other sides of thesquare-shaped beam spot are perpendicular to the sides of the circuitpattern 120. In this case, even if the square-shaped beam spot isslightly shifted (δ) in a horizontal direction, the projection area ofthe laser beam on the circuit pattern 120 is almost not changed. Thus,in the case where the circuit pattern 120 is cut by the laser beam forwhich the mask is adjusted as described above, even if the beam spot ofthe laser beam is slightly shifted, the gap between the cut ends of thecircuit pattern 120 can be uniform (W1=W2).

Further, in the case where the circuit pattern is cut by a laser beam inthe non-contacting manner, the circuit pattern may be scanned by thelaser beam having the square-shaped spot. In this case, as shown in FIG.19, a scanning range (length) of the laser beam is decided so as to begreater than the width W1 of the circuit pattern 120 to be cut. Inaddition, the scanning range of the laser beam is decided so that othercircuit patterns in the same layer as the circuit pattern 120 to be cutand over the circuit pattern 120 are not damaged. That is, the scanningrange of the laser beam is decided so that the length L2 of a projectionarea 133 (133′) is less than the distance W2 between the circuitpatterns 118 and 119 between which the circuit pattern 120 to be cut ispositioned.

In a process in which the insulating body and the circuit patterns arepartially removed by using a high energy beam such as a laser beam or anelectron beam, the deeper in the printed-circuit board, the narrower theregion (the area) to be worked by the high energy beam. The reason forthe above is that the high energy beam is diffracted inside theprinted-circuit board. The degree of variation (narrowing) of the regionto be worked by the high energy beam depends on material of the region.Thus, in a case where the multi-layer printed-circuit board is worked,the projection area (the mask size) of the beam on the surface of theprinted-circuit board is decided based on the thicknesses of therespective layers and the degrees of narrowing of regions to be workedin the respective layers.

For example, a multi-layer printed-circuit board is formed as shown inFIG. 20. Referring to FIG. 20, the printed-circuit board has a firstlayer made of material A (e.g., a resist layer), a second layer made ofmaterial B (e.g., an insulating layer), a third layer (a circuitpattern) made of material C (e.g. copper) and a fourth layer made ofmaterial D. The first layer has the thickness of T_(A), the second layerhas the thickness of T_(B), and the third layer has the thickness ofT_(C) (T=T_(A)+T_(B)+T_(C)). The degree of narrowing of the region to beworked in the respective layers has been previously measured by using alaser beam which is actually used to work the printed-circuit board. Thedegree of narrowing of the region to be worked is represented by anarrowing coefficient (ratio) K. The narrowing coefficient (ration) K ina structure (the first, second and third layers) to be worked is definedbyK=δ/Twhere T is the thickness of the structure to be worked and δ is thedifference between a position of the edge of the projection area of thelaser beam on the surface of the first layer and a position of the edgeof a region to be worked on the bottom surface of the third layer.

In a case where the circuit pattern of the third layer in theprinted-circuit board structured as described above is cut so that a gapof W2 is formed between cut ends of the circuit pattern, the width W1 ofthe projection area (the mask size) of the laser beam (the excimer laserbeam) on the surface of the printed-circuit board (the surface of thefirst layer) is decided as follows. $\begin{matrix}{{W1} = {{{W2} + {2\delta}} = {{W2} + {2\left( {\delta_{A} + \delta_{B} + \delta_{C}} \right)}}}} \\{= {{W2} + {2\left( {K_{A} \times T_{A}} \right)} + {2\left( {K_{B} \times T_{B}} \right)} + {2\left( {K_{C} \times T_{C}} \right)}}}\end{matrix}\quad$

That is, the mask of the laser beam is adjusted so that the projectionarea of the laser beam on the surface of the printed-circuit board hasthe width of W1.

In addition, a working rate R of the laser beam, which is actually usedto work the printed-circuit board, with each of materials of therespective layers has been measured. The working rate R is defined asR=d/Nwhere d is the depth of a hole formed by the laser beam and N is thenumber of times which the laser beam is projected onto the material or atime for which the laser beam is projected onto the material. The numberof times which the laser beam is projected on to each layer (the numberof pulses) or the times for which the laser beam is projected onto eachlayer is controlled based on the working rate R with respect to thematerial of each layer.

The laser beam or the electron beam used to cut the circuit pattern isfocused, as shown in FIG. 21, on the surface of the printed-circuitboard 100 by a lens 160 having a focal length L_(f). If the circuitpattern to be cut is placed at a deep position in the printed-circuitboard, while the region which is worked by the laser beam or theelectron beam is being moved inside the printed-circuit board 100, thedegree of out-of-focus of the laser beam or the electron beam on theworked region is increased. Thus, while the worked region is being movedinside the printed-circuit circuit board, the energy density of thelaser beam or the electron beam on the worked region is decreased, sothat substantial narrowing coefficient (ratio) K of the worked region isincreased. The amount of insulating material which is removed from theworked region by the laser beam is reduced, so that the bottom of theworked hole 134 formed by the laser beam is narrow and curved. As aresult, the gap between cut ends of the circuit pattern located at adeep position in the printed-circuit board 100 is small. That is, thegap is varied in accordance with the position of the circuit pattern inthe depth direction.

To eliminate the above disadvantage, as shown in FIG. 22, the lens 160or a laser head emitting the laser beam is moved in synchronism with themovement of the region which is worked by the laser beam in theprinted-circuit board 100. As a result, while the printed-circuit board100 is being worked by the laser beam, the laser beam is always focusedon the worked region. The movement of the lens 160 or the laser head iscontrolled based on the working rate R of the laser beam with respect tothe material of each of the layers in the printed-circuit board 100.

According to the above control of the lens 160 or the laser head, thebottom of the worked hole 134 can be flat as shown in FIG. 22. As aresult, the variation of the gaps formed in cut circuit patterns in therespective layers of the printed-circuit board can be reduced.

The working rate R of the laser beam depend on the material onto whichthe laser beam is projected. The working rate R with respect to resin ofan insulating body is two or three times as large as the working rate Rwith respect to metal (e.g., copper) of the circuit pattern. In view ofcomplete cutting of the circuit pattern, as shown in FIG. 23A, the widthof the projection area E_(p0) of the laser beam used to work theprinted-circuit board may be greater than the width of the circuitpattern 117 to be cut. In this case, since the working rate with respectto the circuit pattern 117 is smaller than that with respect to theresin of the insulating body, parts of the resin beside the circuitpattern 117 are removed sooner than the circuit pattern 117.

As a result, immediately after the circuit pattern 117 is cut, as shownin FIG. 23B, a protruding portion corresponding to the gap between cutends of the circuit pattern 117 is formed on the bottom surface 135 a ofthe worked hole 135. In an extreme case, before the circuit pattern 117is completely cut, the circuit pattern 101 located under the circuitpattern 117 to be cut is corroded by the laser beam which passes throughportions at the sides of the circuit patterns 117.

To eliminate the above disadvantage, the projection area of the laserbeam is controlled as follows.

Until the surface of the circuit pattern 117 is exposed, the laser beamin which the mask thereof is adjusted so that the projection area E_(p0)is obtained as shown in FIG. 23A is projected onto the printed-circuitboard 100 at the working rate R based on the material of the insulatingbody 103. As a result, as shown in FIG. 25, a worked hole 135, havingthe depth of D₁₁, in which the bottom surface is flat is formed.

After this, as shown in FIG. 24A, the mask of the laser beam is adjustedso that the projection area E_(p1) covering the circuit pattern 117 andonly a portion at a first side of the circuit pattern 117 is obtained.In this state, the laser beam is further projected onto a predeterminednumber of times the bottom surface of the worked hole 135 at the workingrate R with respect the resin of the insulating body 103.

Next, as shown in FIG. 24B, the mask of the laser beam is adjusted sothat the projection area E_(p2) covering the circuit pattern 117 andonly a portion at a second side of the circuit pattern 117 is obtained.In this state, the laser beam is further projected onto the bottomsurface of the worked hole 135 a predetermined number of times at theworking rate R.

After this, every time the laser beam is projected a predeterminednumber of times, the projection area is switched between E_(p1) shown inFIG. 24A and E _(p2) shown in FIG. 24B. The switching operation of theprojection area is continuously performed until the circuit pattern 117is completely cut. During the projection of the laser beam with theswitching operation of the projection area, the depth of the worked hole135 is increased by D₁₂.

According to the projection control of the laser beam, the laser beam isprojected onto the circuit pattern 117 at a rate twice as large as arate at which the laser beam is projected onto both the positions at thefirst and second sides of the circuit pattern 117. In a case where theworking rate with respect to the resin of the insulating body 103 istwice as large as that with respect to the metal of the circuit pattern117, when the circuit pattern 117 is completely cut, positions of workedsurfaces corresponding to the circuit pattern 117 and the portions atthe first and second sides of the circuit pattern 117 in the depthdirection are theoretically the same as each other (D₁₁+D₁₂). As aresult, the protruding portion as shown in FIG. 23B is not formed on thebottom surface 135 a of the worked hole 135 which is formed to cut thecircuit pattern 117. In addition, the circuit pattern 101 located underthe circuit pattern 117 is prevented from being corroded by the laserbeam before the circuit pattern 117 is completely cut.

In the above example, to change the projection area, the mask of thelaser beam is changed. On the other hand, a relative position of theprinted-circuit board to be worked with respect to the laser beam may bechanged in a state where the mask of the laser beam is fixed.

Furthermore, in a case where the working rate with respect to the resincovering the circuit pattern 117 to be cut is greater than twice theworking rate with respect to the circuit pattern 117, a time at whichthe projection area of the laser beam is switched is controlled based onthe difference between the working rates. That is, a switching positionSP at which the projection area of the laser beam is switched in theprinted-circuit pattern is decided so that the bottom surface 135 a ofthe worked hole 135 is substantially flat when the circuit pattern 117is completely cut. As shown in FIG. 26, until the bottom surface of theworked hole 135 reaches the switching position SP (the depth of D₂₁),the printed-circuit board is worked by the laser beam having theprojection area E_(p0) which covers, as shown in FIG. 23, the circuitpattern 117 and the portions at both sides of the circuit pattern 117.After this, in a range between the switching position SP (the depth ofD₂₁) and a position of the depth of D₂₂, the projection area E_(p1)shown in FIG. 24A and the projection area E_(p2) shown in FIG. 24B arealternately switched in the same manner as in the case described above.

As a result of the switching control of the projection area describedabove, even if the working rate with respect to the insulating body 103covering the circuit pattern 117 to be cut is greater than twice theworking rate with respect to the circuit pattern 117, the bottom surface135 a of the worked hole 135 can be flat when the circuit pattern 117 iscompletely cut.

In the cases, as described above, where the circuit pattern is cut byusing the high energy beam such as the laser beam or the electron beamin the non-contacting manner, the metal powder caused by the abrasion ofthe circuit pattern is adhered to the inner surface of the worked hole.As a result, the isolation between the cut ends of the circuit patternmay not be sufficiently maintained.

To prevent such the matter, the projection area of the high energy beamsuch as the laser beam or the electron beam is controlled as follows. Ina case where the circuit pattern in a layer inside the printed-circuitboard is cut by using the excimer laser, as shown in FIG. 27A, the workstarts using the laser beam having the projection area E_(p1) which isgreater than the projection area E_(p3) used to finally cut the circuitpattern 117. The phased adjustment of the mask of the laser beam isperformed so that every time the laser beam is projected a constantnumber of times, the projection area is narrowed (E_(p1)→E_(p2)).Finally, the circuit pattern 117 is cut by using the laser beam havingthe projection area E_(p3), so that the circuit pattern 117 is dividedinto pattern parts 117 a and 117 b. According to the phased control ofthe projection area as described above, the worked hole 136 is, as shownin FIG. 27B, narrowed by stages. In this state, the metal powder causedby cutting of the circuit pattern 117 may be adhered to the innersurface of the worked hole 136.

Next, the mask of the laser beam is adjusted so that the width of theprojection area E_(p4) is slightly greater than the width of theprojection area V_(p1) controlled at the start of the work, as shown inFIG. 28A. The laser beam having the projection area E_(p4) is thenprojected onto an area between the pattern parts 117 a and 117 b apredetermined number of times. Due to the work using the laser beam withthe projection area E_(p4), as shown in FIG. 28B, a slot 136 a deeperthan the worked hole 136 which had been formed is formed. The workedhole 135 is divided into a pattern part 117 a side portion and a patternpart 117 b side portion by the slot 136 a.

The worked hole 136 formed to cut the circuit pattern 117 is divided bythe slot 136 a. While the slot 136 a is being formed, the metal powderadhered to the inner surface of the worked hole 136 is removed. As aresult, there may be no metal powder inside the slot 136 a. Thus, theinsulation between the pattern parts 117 a and 117 b (the cut ends ofthe circuit pattern 117) is prevented from deterioration.

The projection area of the laser beam may be continuously changedinstead of the phased change of the projection area described above.

In this case, the work starts using the laser beam with the projectionarea E_(ps) greater than the projection area E_(pe) finally used to cutthe circuit pattern 117. After this, as shown in FIG. 29A, the mask ofthe laser beam is adjusted so that the projection area is graduallynarrowed in proportion to the number of projections of the laser beam.Finally, the circuit pattern 117 is cut using the laser beam with theprojection area E_(pe), and the circuit pattern 117 is divided into thepattern parts 117 a and 117 b. Due to the continuous control of theprojection area, as shown in FIG. 29B, the worked hole 137 is graduallynarrowed.

In the above case, while the worked hole 137 is being worked, the laserbeam is continually projected onto the inner surface of the worked hole137. Thus, the metal powder generated when the circuit pattern 117 iscut is immediately removed by the laser beam. As a result, theinsulation between the pattern parts 117 a and 117 b can be improved.

To further improve the insulation between the pattern parts 117 a and117 b, after the pattern 117 is cut by the worked hole 137 formed asdescribed above, the projection of the laser beam is performed again asfollows.

The mask of the laser beam is adjusted again so that the width of theprojection area E_(p2) is slightly greater than the width of theprojection area E_(ps) controlled at the start of the work, as shown inFIG. 30A. The laser beam having the projection area E_(p2) is thenprojected onto an area between the pattern parts 117 a and 117 b apredetermined number of times. Due to the work using the laser beam withthe projection area E_(p2), as show in FIG. 30B, a slot 137 a deeperthan the worked hole 137 which has been formed is formed. The workedhole 137 is divided into a pattern part 117 a side portion and a patternpart 117 b side portion by the slot 137 a.

Thus, even if the metal powder is adhered to the inner surface of theworked hole 137, the worked hole 137 formed to cut the circuit pattern117 is divided and the metal powder is removed from the inner surface ofthe slot 137 a. As a result, the insulation between the pattern parts117 a and 117 b is prevented from deteriorating by the powder adhered tothe inner surface of the worked hole 137.

In a case where circuit patterns are altered, a new circuit path isgenerally formed between electronic parts by using a wire. For example,in the case of alteration of the circuit pattern as shown in FIGS. 1A,1B, 1C and 1D, the wire connects the exposed circuit patterns to eachother. If the location of the wire 30 is limited in the printed-circuitboard, a path for electrical connection between two portions is formedin the printed-circuit board as follows.

As shown in FIG. 31, semiconductor devices 11 and 21 (e.g, LSIs) whichare to be electrically connected are mounted on the printed-circuitboard 100. A semiconductor device 31 (e.g., LSI) which is locatedbetween the semiconductor devices 11 and 21 is closely mounted on theprinted-circuit board 100. A groove 131 is formed on the printed-circuitboard 100 under the semiconductor 31 by using the laser beam or theelectron beam. A wire 30 is placed in the groove 131. Ends of the wire30 are connected to predetermined pins of the semiconductor device 11and 21 with solder.

Thus, the wire used for the alteration of the circuit pattern can beplaced inside the printed-circuit board.

As shown in FIG. 32, circuit patterns 101(1) and 101(2) which are insidethe printed-circuit board and respectively connected to pins 12 and 22of semiconductor devices are respectively cut by worked holes 107 and127. A groove 132 is formed, by using the laser beam, on theprinted-circuit board between the circuit pattern 100(1) connected withthe pin 12 and the circuit pattern 100(2) connected with the pin 22. Atthe ends E₁ and E₂ of the groove 132, the circuit patterns 100(1) and100(2) are partially exposed. The wire 30 is placed in the groove 132.The ends of the wire 30 are respectively connected to the exposedportions of the circuit patterns 100(1) and 100(2) with solder.

In addition, as shown in FIG. 33, the groove 132 formed in the samemanner as in the above case is filled with conductive material 310, suchas solder paste, solder wire, solder ribbon, solder balls or conductiveadhesive. The whole printed-circuit or the groove is heated so that theconductive material 310 is melted and subsequently hardened. As aresult, the circuit patterns 100(1) and 100(2) which are partiallyexposed at the ends E₁ and E₂ of the groove 132 are electricallyconnected by the conductive material 310 filling the groove 132.

The wire 30 and the conductive material 310 provided in the groove 132formed on the printed-circuit board are fixed in the groove 132,insulated and protected as follows.

As shown in FIG. 34A, the inner surface of the groove 132 is coated withfixing material 311, such as adhesive, coating material or pottingmaterial. While the fixing material 311 is heated, the wire is placed inthe groove 132. As a result, as shown in FIG. 34B, the wire 30 can befixed, insulated and protected by the fixing material 311 (the adhesive,coating material or potting material).

Furthermore, after the wire 30 or the conductive material (e.g., thesolder, the conductive adhesive or the like) is provided in the groove132, the groove 132 may be filled with the fixing material 311 (theadhesive, the coating material or the potting material). The fixingmaterial filling the groove 132 is then hardened. In this case also, thewire 30 or the conductive material can be fixed, insulated and protectedby the fixing material as shown in FIG. 34B.

In addition, the wire 30 can be fixed in the groove 132 formed on theprinted-circuit board as follows.

As shown in FIG. 35A, the wire 30 which is coated with fusion material312 is placed in the groove 132 formed in the printed-circuit board 100.The fusion material 312 reveals adhesiveness when the fusion material312 is heated or is provided with solvent. After the wire 30 is placedin the groove 132, the wire 30 is heated or provided with the solvent.The fusion material 312 is thus softened and the wire 30 is fixed in thegroove 132 by the fusion material 312.

The present invention is not limited to the aforementioned embodiments,and other variations and modifications may be made without departingfrom the scope of the claimed invention.

1. A method for cutting a circuit pattern inside a printed-circuit boardby an energy beam comprising the steps of: (a) adjusting a mask of saidbeam so that a projection area of said beam projected onto a surface ofsaid printed-circuit board has a predetermined length in a directionparallel to a width direction of said circuit pattern; and (b)projecting said beam onto said printed-circuit board so that a hole isformed in said printed-circuit board, whereby said circuit pattern iscut by said beam.
 2. A method for cutting a circuit pattern inside aprinted-circuit board by an energy beam comprising the steps of: (a)adjusting a mask of said beam having a predetermined energy so that aprojection area of said beam is formed on a surface of saidprinted-circuit board, the projection area being decided based on anarrowing ratio of said beam and a working area of said beam projectedonto a surface of said circuit pattern to be cut, the narrowing ratio ofsaid beam being a degree of narrowing of an area to be worked by saidbeam having the predetermined energy in materials on and over a surfaceof said circuit pattern; and (b) projecting said beam in which said maskthereof is adjusted on said printed-circuit board so that a hole isformed in said printed-circuit board, whereby said circuit pattern iscut by said beam.
 3. A method for cutting a circuit pattern inside aprinted-circuit board by an energy beam comprising the steps of: (a)removing a portion of said printed-circuit board by projection of saidbeam focused on a focal point; and (b) moving the focal point on whichsaid beam is focused with moving of a working area of said beams insidesaid printed-circuit board caused by removing the portion of saidprinted-circuit board whereby said circuit pattern is cut by said beam.4. A method for cutting a circuit pattern inside a printed-circuit boardby an energy beam comprising the steps of: (a) projecting said beam inwhich a mask thereof is adjusted so that a first projection area of saidbeam corresponds to an area covering said circuit pattern, a firstportion at a first side of said circuit pattern and a second portion ata second side of said circuit pattern, a hole worked by said beam beingformed until a predetermined depth is obtained; (b) projecting said beamin which the mask thereof is adjusted so that a second projection areaof said beam corresponds to an area covering said circuit pattern andthe first portion; (c) projecting said beam in which the mask thereof isadjusted so that a third projection area of said beam corresponds to anarea covering said circuit pattern and the second portion, wherein aftersaid step (a) is completed, said step (b) and said step (c) arealternately repeated at predetermined intervals until said circuitpattern is cut by said beam.
 5. A method for cutting a circuit patterninside a printed-circuit board by an energy beam comprising the step of:projecting said beam on said printed-circuit board while a mask thereofis being adjusted so that a projection area of said beam is graduallynarrowed, a hole being formed in said printed-circuit board byprojection of said beam, so that said circuit pattern is cut by saidbeam.
 6. The method as claimed in claim 5, wherein the projection areaof said beam is narrowed by stages.
 7. The method as claimed in claim 5,wherein the projection area of said beam is continuously narrowed. 8.The method as claimed in claim 5, further comprising the step of:working an inner surface of said hole by said beam in which the maskthereof is adjusted so that a projection area crosses an area betweencut ends of said circuit pattern which has been but by said beam.